When keeping ornamental fish, such as, e.g., saltwater fish or freshwater fish, in an aquarium, a filtering device is generally installed for the purpose of keeping the water in the aquarium clean.
As an aquarium filtering device, an underwater installation type filtering device designed to be installed within an aquarium and an outside installation type filtering device designed to be installed outside an aquarium are well known. As compared with the underwater installation type filtering device, the outside installation type filtering device is suitable in terms of enlarging the size and can have excellent filtration capacity.
Conventionally, for the purpose of supplying the water in the aquarium to an outside installation type filtering device or returning the water in the filtering device to the aquarium, an overflow device is used.
As disclosed in the following Patent Document 1, a conventional overflow device includes a tank-outside water storing portion to be disposed on the side wall outside surface of an aquarium, and an inverted U-shaped siphon pipe to be disposed so as to straddle the aquarium inside and the aquarium outside, and an overflow pipe provided in the tank-outside water storing portion. It is configured such that the water in the aquarium is supplied to the tank-outside water storing portion via the siphon pipe and flows out via the overflow pipe to be supplied to a filtering device disposed outside the aquarium.
The filtering device disposed outside the aquarium is provided with a discharge pump so that the water filtered by the filtering device is forcibly discharged (returned) by the discharge pump to the aquarium via an outlet pipe.    Patent Document 1: Japanese Utility Model Registration No. 3018619 (FIG. 3)